The invention relates to a process for manufacturing a cooling channel piston.
Using a casting or forging process, it is basically known to manufacture blanks for pistons which include a cooling channel after their final machining. Combinations of the two aforementioned processes are also possible. The forging process suggests itself since a piston manufactured by forging has superior strength characteristics compared with a piston manufactured by casting. In the case of piston blanks manufactured by forging, a complex process is required to introduce a cooling channel into this piston blank in the area of the ring belt. In contrast to cast piston blanks, the lost core process cannot be employed with blanks produced by forging. Consequently, introducing the cooling channel using suitable steps causes a recurring problem. The known methods are to introduce a radially circumferential recess through machining by metal-cutting methods and then to close said recess using suitable means. In so doing, close attention must be paid to the dimensional accuracy of the recess and the means that are intended to close this recess. The result is that an additional cost-intensive procedure is required. Because of the necessary dimensional accuracy, it is correspondingly complex to produce the elements involved.
A generic procedure is known from DE 35 02 248 C1 for manufacturing a single-piece piston for a combustion engine by forging. In this process, a piston blank is manufactured having a pre-form collar, where this collar is turned down in the upper area of the piston crown by bending over, creating a piston crown shoulder, which together with an area of a piston crown pre-form creates an annular thermally inhibiting gap. Because the collar is bent over in the upper areas of the piston crown, rounded edges are created initially which require reworking of the lateral and top surfaces of the piston blank. A substantial disadvantage additionally results from the bending, which weakens the piston crown so that a piston manufactured in this way is no longer adequate to meet the demands of modern combustion engines with respect to increased ignition pressures and combustion temperatures required to meet exhaust emissions requirements.
The object of the invention is, therefore, to propose a procedure for manufacturing a piston in which the cooling channel can be produced simply and easily.